This invention relates to resinous coating compositions comprising blends of hydroxyfunctional polymers or copolymers, alkoxysilane crosslinking agents and cure accelerating catalysts.
Organo-silicon compounds such as polyorganosiloxanes, polysilanols and organoalkoxysilanes have previously been utilized in prior art resinous coating compositions to provide films having superior durability, e.g., see U.S. Pat. Nos. 3,318,971, 3,468,836, 3,644,566, 3,668,272, 3,707,518, 3,707,709 and 3,816,164. However, in the prior art resinous coating compositions as exemplified by the above patents such organo-silicon compounds were incorporated into the resin polymer by polymerizing the organo-silicon compound with the resin monomer to produce a silicon-containing copolymer or interpolymer. In another method exemplified in the above patents i.e., U.S. Pat. No. 3,318,971 and 3,468,836, the organo-silicon compound is incorporated into the resin by partially condensing a hydroxyfunctional acrylic polymer with a silicon containing material such as a polysilanol or a polyorganosiloxane to form a single phase or unitary resin. In any event, the above-mentioned prior art patents teach resinous coating compositions in which the organo-silicon compound is incorporated into or chemically bonded to the resin polymer. These patents do not teach or suggest resinous coating compositions in which a resinous polymer is physically blended with an organo-silicon compound and in fact teach that the physical blending of an organosilicon compound with a resin polymer is undesirable. Thus, U.S. Pat. Nos. 3,318,971 and 3,668,272 teach that the physical blending of silicon-containing resins with commercially available acrylic resins was without significant benefit or success and that small proportions of silicon-containing resins used in such blends accomplished little while larger proportions of silicon-containing resins degraded the cure of the acrylic resins and films produced from such blends were brittle and of limited utility. The necessity of incorporating the organo-silicon compound into the resin polymer by polymerization or condensation to form a useful coating composition which when crosslinked by curing produces a film exhibiting good physical properties presents obvious disadvantages. Thus, polymerization reactions often require extensive equipment and control procedures while in condensation reactions an intermediate is often formed which requires an additional processing step before the intermediate can be incorporated into the resin polymer. Moreover, as indicated previously, in several of the prior art coating compositions exemplified in the above patents an additional crosslinking agent such as an aminoplast resin is employed to provide a highly crosslinked film having good physical properties.
Accordingly, it would be highly advantageous if a resinous coating composition containing an organo-silicon compound could be formulated by physically blending or admixing the resin polymer with the organo-silicon compound at ambient temperature in conventional mixing equipment to produce a silicon-containing resinous coating composition which would not require an additional crosslinking agent and yet which upon curing produces a film having good physical properties. The coating compositions of this invention possess this capability.